This invention relates to a power supply device having a function of notifying an electronic equipment of the secondary side that input power to the primary side is disconnected abnormally, for example, by service interruption, disconnection of a power supply cable or compulsory disconnection by means of a breaker.
An electronic equipment which operates with an AC (alternating current) power supply like power supply for domestic use such as, for example, a television set, a video apparatus, an audio apparatus or a personal computer normally includes an AC-DC power supply device for converting AC power supply into DC (direct current) power supply in order to allow operation of an internal control circuit and so forth.
An electronic equipment of the type described sometimes suffers from abnormal disconnection wherein inputted AC power supply is disconnected suddenly during use thereof because of “pulling out of a plug for AC power supply”, “compulsory disconnection of AC power supply by means of a breaker” or “occurrence of service interruption”.
If such abnormal disconnection of AC power supply occurs in an electronic equipment which requires storage or backup of process data upon disconnection of power supply such as, for example, a personal computer or a digital television receiver, then the electronic equipment may not be able to perform an ending process such as storage or backup of process data, and there is the possibility that it may suffer from a failure or incomplete operation after the abnormal disconnection.
Therefore, a power supply device for use with an electronic equipment of the type described normally includes an abnormal disconnection detection circuit which detects a power drop state of the secondary side, estimates that abnormal disconnection may occur and stop the supply of power and notifies the equipment of the estimated stop of power supply. Since the power supply device includes an abnormal disconnection detection circuit of the type just described, the electronic equipment can perform an ending process such as storage or backup of process data into a non-volatile memory before the power supplied to the secondary side stops completely and consequently can prevent an otherwise possible failure or incomplete operation caused by such abnormal disconnection.
A first related art power supply device which includes a detection circuit for detecting abnormal disconnection is described.
A configuration of the first related art power supply device is shown in FIG. 4.
The related art power supply device 101 includes an input terminal 111 for receiving, for example, a domestic input AC voltage (VAC), an inputting switch 112 for performing switching on/off of the AC input, a power supply section 113 for converting the input AC voltage (VAC) into a stabilized DC voltage (output DC voltage: VDC), and a detection section 114 for detecting abnormal disconnection of the AC input. The first related art power supply device 101 just described converts the input AC voltage (VAC) supplied as domestic power thereto into the stabilized output DC voltage (VDC) and can supply the stabilized output DC voltage (VDC) to an electronic equipment, in the following stage, such as a personal computer, a digital TV receiver or the like.
The detection section 114 monitors a secondary side output DC voltage (VDC) outputted from the power supply section 113. If the secondary side output DC voltage (VDC) drops, that is, if abnormal disconnection occurs, then the detection section 114 turns ON a detection pulse (r) and notifies an electronic equipment in the following stage of the abnormal disconnection.
For example, the detection section 114 can be implemented with such a circuit as shown in FIG. 5. The detection section 114 is formed from a diode 121 which receives, at the anode thereof, the output DC voltage (VDC) from the power supply section 113, a capacitor 122 whose one end is connected to the cathode of the diode 121 while the other end is connected to the ground, a pnp transistor 123 whose emitter is connected to the cathode of the diode 121, a first resistor 124 whose one end is connected to the anode of the diode 121 while the other end is connected to the base of the pnp transistor 123, and a second resistor 125 whose one end is connected to the collector of the pnp transistor 123 while the other end is connected to the ground.
The detection section 114 having such a configuration a described above generates the detection pulse (r) from the collector of the pnp transistor 123. The detection pulse (r) exhibits ( ) (volt) in a steady state wherein the output DC voltage (VDC) is stabilized. If the output DC voltage (VDC) drops by a predetermined voltage (ΔV) from the voltage of the steady state, then the detection pulse (r) rises up to the predetermined voltage and turns ON.
Operation of the first related art power supply device 101 is described with reference to FIG. 6.
Since the power supply device 101 holds, at the power supply section 113 thereof, residual power after the input AC voltage (VAC) stops (at time t101), the output DC voltage (VDC) is continuously outputted to the secondary side for a while. If the residual power decreases, then dropping of the output DC voltage (VDC) is started. Here, if the output DC voltage (VDC) drops by the predetermined voltage (ΔV) from the voltage of the steady state (at time t102), then the pnp transistor 123 of the detection section 114 turns ON and the detection pulse (r) turns ON. The detection pulse (r) is conveyed to the electronic equipment side. The electronic equipment performs an ending process including storage or backup of process data or the like when the detection pulse (r) turns ON.
The first related art power supply device 101 having such a configuration as described above monitors a voltage dropping state of the secondary side output DC voltage (VDC) of the power supply section 113 and notifies the electronic equipment side of the state. Consequently, in the power supply device 101, the time (tf1) which can be used for an ending process from time (t102) at which the detection pulse (r) turns ON to time (t103) at which a voltage value (VTH) necessary for performing the ending process is obtained is very short. Consequently, it is difficult that the first related art power supply device 101 is used for an electronic equipment such as a personal computer or a digital broadcast receiver, wherein an ending process time is relatively long.
Generally, an AC-DC power supply device of the switching inverter type is used as a power supply device for use with an electronic equipment. In the power supply device of the switching inverter type, since the residual power held therein is high and the power conversion efficiency is high, the residual time within which the secondary side output DC voltage continues to be outputted is long after the AC input is disconnected. Consequently, if abnormal disconnection of the AC input is detected more quickly, then the time which can be used for the ending process by the electronic equipment can be extended longer.
A second related art power supply device of the switching inverter type which includes a detection section which can detect such abnormal disconnection of the AC input as described above more quickly is described.
A configuration of the related art power supply device of the switching inverter type is shown in FIG. 7.
Referring to FIG. 7, the related art power supply device 201 shown includes an input terminal 211 to which, for example, a domestic input AC voltage (VAC) is inputted, an inputting switch 212 for switching on/off the AC input, a switching power supply section 213 for converting the input AC voltage (VAC) into a stabilized DC voltage (output DC voltage: VDC), a synchronism detection section 214 for generating a synchronization pulse (P) synchronized with the input AC voltage (VAC), and a control section 215 for detecting abnormal disconnection of the AC input based on the synchronization pulse (P) generated from the synchronism detection section 214.
Though not shown, the switching power supply section 213 includes a rectification circuit which rectifies, for example, the input AC voltage (VAC) into a DC voltage once, a transformer wherein the DC voltage outputted from the rectification circuit is inputted to the primary side coil, a smoothing circuit for smoothing an output voltage from the secondary side coil of the transformer, and a switching circuit which performs switching of input current supplied to the primary side coil.
The switching power supply section 213 having such a configuration as just described performs, for example, PWM (Pulse Width Modulation) control of switching in response to a voltage value of the secondary side output DC voltage (VDC) so that the secondary side output DC voltage (VDC) may be stabilized. The second related art power supply device 201 having such a configuration as described above can convert the input AC voltage (VAC) supplied thereto as domestic power into the stabilized output DC voltage (VDC) and supply it to an electronic equipment including a personal computer, or a digital TV receiver.
The detection section 214 detects the input AC voltage (VAC) inputted thereto from the input terminal 211 and generates the synchronization pulse (P) synchronized with the input AC voltage (VAC). The control section 215 monitors the synchronization pulse (P) outputted from the detection section 214 and generates a detection pulse (r) to be conveyed to the electronic equipment in the following stage when the generation of the synchronization pulse (P) stops for more than a predetermined period of time.
Operation of the second related art power supply device 201 is described with reference to FIG. 8.
The detection section 214 generates a pulse synchronized with the input AC voltage (VAC). Accordingly, upon steady operation, the synchronization pulse (P) which has a frequency of, for example, 60 Hz is generated from the detection section 214.
If the input AC voltage (VAC) is disconnected abnormally (at time t201), also the generation of the synchronization pulse (P) stops. However, since residual power is held in the power supply section 213 also after the supply of the input AC voltage (VAC) stops, the output DC voltage (VDC) continues to be outputted to the secondary side for a little while. If the predetermined time (Δt) passes after the stop of the generation of the synchronization pulse (P), then the control section 215 turns ON the detection pulse (r). The detection pulse (r) is conveyed to the electronic equipment side. When the detection pulse (r) turns ON, the electronic equipment performs an ending process such as storage or backup of process data.
Accordingly, different from the First related art power supply device 101 described above, the second related art power supply device 201 directly monitors the input AC voltage (VAC) and discriminates whether or not the input AC voltage (VAC) is disconnected abnormally. Consequently, the second related art power supply device 201 can convey the abnormal disconnection to the electronic equipment side before the output of the DC voltage (VDC) drops. Therefore, the abnormal disconnection can be conveyed more quickly than the first related art power supply device 101. Consequently, in the second related art power supply device 201, the time (tf2) which can be used for the ending process by the electronic equipment from the time (t202) at which the detection pulse (r) turns ON to the time (t203) at which the voltage value (VTH) necessary for performing the ending process is obtained can be made longer. Further, the second related art power supply device 201 can cope with an electronic equipment including a personal computer or a digital broadcast receiver, wherein the ending process time is relatively long.
However, in a power supply device of the switching inverter type, the primary side and the secondary side must be isolated from each other in order to assure the safety. Therefore, the input AC voltage (VAC) inputted to the detection section 214 and the synchronization pulse (P) outputted from the detection section 214 must be signals isolated from each other in terms of the circuit. Therefore, in the second related art power supply device 201, a transformer must be provided in the detection section 214 to isolate the input AC voltage (VAC) and the synchronization pulse (P) from each other, resulting in increased circuit area. Further, even if, for example, a photo-coupler or the like is used in place of a transformer, since the photo-coupler itself must be driven with DC, high power loss occurs with voltage conversion for the AC/DC conversion.